The present invention relates to a voltage controlled oscillator and in particular to a voltage controlled oscillator in which a surface acoustic wave device is coupled as a feedback element or network to a driving means such as an amplifier to form the oscillator circuit and having an adjustable voltage control coupled to the amplifier for varying the phase shift of the amplifier output over a predetermined range to cause the oscillator circuit to oscillate at a predetermined frequency within a predetermined range.
Oscillators are well-known in the art and phase shift oscillators have been formed utilizing surface acoustic wave devices. U.S. Pat. No. 3,950,713 discloses a surface acoustic wave delay line for use with an amplifier to form an oscillator circuit. The surface acoustic wave delay line oscillator disclosed in this patent is for operation at relatively low frequencies since, as pointed out therein, at high frequencies reflection problems become so pronounced that alternative techniques must be used. It has a frequency which depends upon the construction of the surface acoustic wave delay line. U.S. Pat. No. 3,868,595 also discloses a surface acoustic wave delay line oscillator operating at UHF frequencies. In this case, the inputs and outputs of the amplifier and the surface acoustic wave device must be coupled to matching networks including inductors, capacitors and resistors. Again, the oscillator operates at a frequency depending upon the construction of the surface acoustic wave delay line and its matching networks.
The present invention relates to a solid state voltage controlled oscillator circuit which utilizes a surface acoustic wave device as the signal feedback network and which includes a driving means such as an amplifier having a signal input and a signal output and having a predetermined signal phase shift between its output and input. By coupling an adjustable voltage means to the amplifier for varying the phase shift of the amplifier output over a predetermined range, the circuit can be caused to oscillate at a predetermined frequency within the predetermined range. Such voltage controlled oscillator is relatively inexpensive, very small and compact and meets the requirements for stable oscillators which are shock insensitive and temperature insensitive. This is the case because it can be used at high frequencies but does not include inductors, or capacitors thus providing a relatively shock insensitive and temperature insensitive voltage controlled oscillator whose temperature sensitivity is primarily dependent upon the surface acoustic wave device characteristics.